The invention relates to a shoe having a sole structure and an air pump device for blowing air into the interior of the shoe, the air pump device comprising a bellows made from an elastic plastic material, formed in the sole structure and surrounding a cavity, an intake channel for transporting air from an intake opening into the bellows, and an air supply device formed in the sole structure for forwarding air from the bellows into the interior of the shoe.
Such a shoe is known for example from the documents EP 2 218 348 A1 and WO 2012/126489 A1. In the known shoes of the kind described above, the sole structure may have a multilayer construction in the heel area, wherein an intermediate layer containing the cavity is made from a material (soft polyurethane foam for example) that is intended to be more elastic or more compressible than the material of the outsole. The cavity and the compressible plastic layers that surround it form a bellows. The air pump device is designed so that, in an alternating manner in response to a walking movement of a user, air is sucked into the cavity of the bellows from outside the shoe via the air intake channel when a load is removed (the shoe is lifted off the ground) and air is blown out of the bellows into the shoe interior through channels of an air supply device when a load is applied (when the shoe comes into contact with the ground and supports the user's weight). A first valve is arranged in the air intake channel and is designed to allow air to pass only in the direction from outside the sole structure into the cavity. A second valve is arranged in the air supply device, and is designed to allow air to pass only in the direction from the cavity to the channels. The pump effect is supported further still by the outsole having a raised area in the region of the bellows on the outer tread, which area is pressed toward the upper part of the sole when the load of the user's foot is placed upon it. The teaching of EP 2 218 348 A1 includes the suggestion to arrange the intermediate sole between a hard outsole and a further sole, wherein the intermediate sole should be manufactured from a material that is more compressible (more elastic/softer) than that of the outsole and the further sole.
In order to achieve good ventilation of the shoe interior, that is to say effective airflow, it is essential that during walking at each step, on the one hand, a sufficiently large quantity of air is sucked into the bellows from the outside and on the other hand that it is then blown out of the bellows into the shoe interior. In order for the greatest possible quantity of air to be blown into the shoe interior when the load is applied during each step, not only must the volume of the bellows be maximized; it must also be ensured that when the load is applied, the bellows is compressed almost completely, or at least to a great degree, so that the air contained is forced out. Complete or substantial compression can be achieved by making the sole structure surrounding the cavity very supple or soft, so that it is completely compressed by the effect of the bodyweight. However, the bellows must also expand and fill with air as completely as possible thereafter, when the user lifts the foot with the shoe, and before the next treading (in the next step). Such a restoring action is achieved with a sole material surrounding the cavity that is as elastically hard as possible. However, this conflicts with the previously stated requirement for a soft material.
In order to support the restoration of the bellows, from EP 1 093 729 A1 and EP 0 624 322 A1 for example, it is known to arrange helical springs vertically inside the cavity in such manner that they are compressed when the bellows is compressed. These constructions are expensive to make, they require a relatively large installation space, and in shoes that are exposed to heavy use they have a short service life.